An ink jet printer of the type frequently referred to as drop-on-demand, has at least one printhead from which droplets of ink are directed towards a recording medium. Within the printhead, the ink is contained in a plurality of channels. Piezoelectric devices or power pulses cause the droplets of ink to be expelled as required, from orifices or nozzles located at the end of the channels. In thermal ink jet printing, the power pulses are usually produced by resistors also known as heaters, each located in a respective one of the channels. The heaters are individually addressable to heat and vaporize the ink in the channels. As a voltage is applied across a selected heater, a vapor bubble grows in that particular channel and ink bulges from the channel nozzle. At that stage, the bubble begins to collapse. The ink within the channel retracts and then separates from the bulging ink thereby forming a droplet moving in a direction away from the channel nozzle and towards the recording medium whereupon hitting the recording medium a spot is formed. The channel is then refilled by capillary action which, in turn, draws ink from a supply container of liquid ink.
The ink jet printhead may be incorporated into either a carriage type printer or a page width type printer. The carriage type printer typically has a relatively small printhead containing the ink channels and nozzles. The printhead is usually sealingly attached to a disposable ink supply cartridge and the combined printhead and cartridge assembly is attached to a carriage which is reciprocated to print one swath of information (equal to the length of a column of nozzles) at a time on a stationary recording medium, such as paper or a transparency. After the swath is printed, the paper is stepped a distance equal to the height of the printed swath or a portion thereof so that the next printed swath is overlapping or contiguous therewith. The procedure is repeated until the entire page is printed. In contrast, the pagewidth printer includes a stationary printhead, also known as a printhead assembly, having a length sufficient to print across either the entire width or length of the recording medium. The recording medium is continually moved passed the pagewidth printhead in a direction normal to the length of the printhead and at a constant or varying speed during the printing process.
It has been recognized that there is a need to maintain the ink ejecting nozzles of an ink jet printhead, for example, by periodically cleaning the orifices when the printhead is in use, and/or by capping the printhead when the printer is out of use or is idle for extended periods of time. The capping of the printhead is intended to prevent the ink in the printhead from drying out. There is also a need to prime a printhead before use, to insure that the printhead channels are completely filled with ink and contain no contaminants or air bubbles and also periodically to maintain proper functioning of the orifices.
It has been found that to properly maintain an ink jet printhead two separate operations must be performed, using usually two separate, technician serviceable devices, namely, a maintenance assembly, and a capping assembly. In a first operation, the maintenance assembly is typically used to maintain proper condition or operation of the printhead nozzles by priming the nozzles such as by vacuum, and wipe cleaning clean the face of the printhead to remove any contaminants or ink which may have collected thereon. The second and separate operation is capping the printhead during periods when the printhead nozzles will be exposed to air for extended periods, thereby preventing the ink contained in the nozzles from drying out.
Conventionally, maintenance assemblies and capping assemblies are serviced (including replacement), not by the machine operator, but by a technician. Where a fluid is needed by each of these assemblies, such fluids are usually not common, and are supplied separately, thus involving several costly parts and components. Long printing periods (during which a capping assembly is exposed and idle), can result in warping of the capping assembly seals, as well as in poor printhead capping, thus requiring replacement of the capping assembly.
There is therefore a need for an ink jet printer in which the design and operation of the maintenance assembly and the capping assembly have a number of parts in common thus reducing their costs, and in which the capping assembly is economically and easily replaceable by an operator, thus assuring continued quality operation of the printhead.